Radiation therapy is widely used in cancer therapy and is also indicated for several other health conditions. Conventionally, a radiation therapy treatment plan (also referred herein as a treatment plan) for a cancer patient is generated before treatment starts. The treatment plan may be delivered to the patient during several treatment fractions, spread over a treatment period of multiple days. However, during the treatment period, the anatomy of the tumor or other tissues (e.g., tissue surrounding the tumor) may change. For example, the tumor may grow, deform, or shrink. Accordingly, the treatment plan may need to be updated. Thus, it may be desirable to develop systems and methods for adapting a treatment plan during the course of the treatment period.